Financial transactions are a crucial part of our everyday lives. On one end, there are financial transactions between merchants and customers. On the other end, there are financial transactions between customers. When two or more customers want to share the cost of a purchase, apportioning the cost between them can be difficult, especially when one or more of them want to pay by credit card. Consider, for example, the situation in which a social group gathers for a meal at a restaurant, where everyone is to pay for his or her own food and drink. When it comes the time to pay the check, the need of conducting payment from one party to another can create an inconvenient and sometimes awkward interruption in the social interaction of the group. When there is not enough cash in the social group to settle the bill, many customers also find annoying the need to remember and track down how much each party owes to another.